It is widely accepted that both acute and chronic exercise alter the number and function of circulating cells of the innate immune system (e.g., neutrophils, monocytes and natural killer (NK) cells). Similarly, it is agreed that a lymphocytosis is observed during and immediately after exercise, proportional to exercise intensity and duration, with the number of cells (T cells and to a lesser extent B cells) falling below pre-exercise levels during the early stages of recovery, before returning to resting values normally within 24 hours. Finally, a consensus exists that reduced levels of secretory immunoglobulin A (SIgA) are associated with increased risk for URTI during heavy training as the production of SIgA is the major effector function of the mucosal immune system providing the ‘first line of defense’ against pathogens. Thus, there is an ongoing need to manage and reduce the negative effects of exercise on the immune system to keep athletes healthy and performing at their highest levels.